1. Field of the Invention
The present general inventive concept relates to a paper picking-up unit and an image forming apparatus having the same, and more particularly, to a paper picking-up unit having an improved structure in which noise occurring during a paper picking-up operation is reduced, and an image forming apparatus having the same.
2. Description of the Related Art
In general, an image forming apparatus, such as a printer or copier, includes a paper picking-up unit which receives a plurality of papers, picks up each of the plurality of received papers and supplies the picked-up paper into a main body of the image forming apparatus. FIGS. 1 and 2 are perspective views of an example of a conventional paper picking-up unit. FIG. 1 shows a state just before a paper is picked up, and FIG. 2 shows the instant the paper is picked up.
Referring to FIGS. 1 and 2, a conventional paper picking-up unit 10 comprises a knock-up plate 12, which is coupled with a hinge 14 to a paper feeding cassette (not shown) mounted in a main body (not shown) of an image forming apparatus, and on which a paper P is stacked, a spring 18 which elastically biases the knock-up plate 12 in an upward direction, and a pick-up roller 20, which is disposed in the main body (not shown) of the image forming apparatus and positioned on the knock-up plate 12.
The pick-up roller 20 comprises a roller body 21, which is engaged with a shaft 28 for transferring a rotative power when rotated, has a generally semicircular shape and includes a frictional layer generally formed of rubber and disposed on an outer circumference of the roller body 21 so as to pick up the paper P, and a roller housing 25 which supports both sides of the roller body 21 so that the roller body 21 does not move in a lengthwise direction of the shaft 28.
A pair of cams 30 are engaged with both sides of the shaft 28 in the state where the pick-up roller 20 is placed between the pair of cams 30. The cams 30 press both sides of the knock-up plate 12 in a printing standby state and separate a front end of the paper P from the pick-up roller 20.
If a printing instruction is input into an image forming apparatus (not shown), the pick-up roller 20 and the cam 30 rotate in the direction of arrows shown in FIGS. 1 and 2 by rotation of the shaft 28, and as shown in FIG. 2, the knock-up plate 12 pressed by the cam 30 in a downward direction rotates around the hinge 14 by elasticity of the spring 18 when the cam 30 is removed, and the front end of the knock-up plate 12 apart from the hinge 14 rises. As such, the front end of the paper P stacked on the knock-up plate 12 contacts the roller body 21 of the rotating pick-up roller 20, is picked up by friction with the frictional layer disposed on the outer circumference of the roller body 21, and is fed into the main body (not shown) of the image forming apparatus.
However, the knock-up plate 12 collides with an outer circumference of the roller housing 25 when the knock-up plate 12 rises, resulting in noise. This noise continues until a printing operation is terminated when several papers are printed continuously, and is disturbing to a user.
In particular, if a small number of the papers P are stacked on the knock-up plate 12, shocks that occur when the knock-up plate 12 collides with the roller housing 25 are not reduced, and noise becomes more severe. In addition, due to the shocks, the paper P may be deviated from its registered position, and jam or skew of the paper P may occur.